uboot-imx

scripts: Add script to extract default environment

This script looks for env_common.o object file and extracts from it default
u-boot environment, which is afterwards printed on standard output.

Usage example:
get_default_envs.sh > u-boot-env-default.txt

The generated text file can be used as input for mkenvimage.

Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
Reviewed-by: Simon Glass <sjg@chromium.org>